When your flat roof in Cromer needs replacing or repairing, knowing exactly what the job involves from start to finish helps you ask the right questions and spot a quality installation.
Call any time. Calls are answered day and night and passed straight to our roofers.
A flat roof replacement is not a single task - it is a sequence of steps, and each one has to be done correctly for the next to work. Whether the roof covers an extension, a garage, or an outbuilding, the process follows the same broad order. Understanding that order means you can follow what is happening on your property and hold any roofer to account if something looks wrong.
We cover Cromer and the surrounding North Norfolk coast for flat roofing work, installing and repairing roofs using EPDM rubber membrane and traditional mineral felt systems. Below is a plain account of how a flat roof job runs from the first visit to the clean-up.
Before any price is agreed, the roof needs to be looked at properly. A visual inspection from ground level is not enough. The roofer should get up and walk the roof surface, check the falls (the slope that drains the roof), look at the condition of the deck beneath, and inspect where the roof meets any walls, upstands, or parapet walls.
Common problems to look for at this stage include ponding water, blistering or cracking of an old felt surface, soft or spongy spots in the deck (which indicate rotting timber below), failed lap joints where sheets of felt have pulled apart, and blocked or inadequately sized outlets. On older properties, the deck is often tongue-and-groove boarding, which can cup, split, or rot in patches. On extensions built from the 1970s onwards, you are more likely to find chipboard, which swells badly when wet and needs replacing rather than patching if water has got in.
The survey should result in a clear written description of what needs doing and why. If a roofer cannot explain the condition of your deck and what they propose to do with it, ask again before agreeing to anything.
Once the job starts, the first physical work is stripping back to the deck. On a felt roof, that means removing all layers of felt, any old insulation boards, and the battens or drip edges around the perimeter. This is a dusty, disruptive stage and debris needs somewhere to go - skips or large bags, agreed before the job starts.
Once the old covering is off, the deck can be properly assessed. Rot or delamination that was not obvious during the survey sometimes becomes clear only at this point. A good roofer will show you any problem areas before carrying on, because replacing sections of decking adds cost and you deserve to understand why before the bill changes.
All old fixings, nails, and staples should be removed or punched flush. Any surface left proud will eventually telegraph through a new membrane and create a weak point.
If the decking is sound, it is prepared and cleaned. If sections have rotted, they are cut out and replaced with new OSB (oriented strand board) or exterior-grade plywood, both of which are more stable than the chipboard used in older builds. The deck needs to be solid, level, and free of movement before anything goes on top of it.
Falls should be checked at this stage too. A flat roof is never truly flat - it needs a minimum fall of 1:80 to drain properly, though 1:40 is better practice. On older roofs, the falls were sometimes inadequate from day one, and standing water is the result. If the deck is being replaced anyway, it is worth asking whether firring pieces (tapered timber strips) can be added to improve drainage. It is much harder to address this once the new covering is on.
Modern flat roofs are built as warm roofs, with insulation placed above the deck rather than between the joists. This avoids the condensation problems that plagued the cold roof designs common in older builds, where insulation sat below the deck and moisture would gather in the void above it.
In a warm roof build-up, rigid insulation boards - typically PIR foam boards - are laid on top of the prepared deck. The thickness of the insulation affects both the thermal performance of the roof and the overall height at the eaves and at any abutting walls. Typical insulation thicknesses range from 50mm to 150mm depending on the U-value required. Current building regulations for new extensions and replacements require a U-value of 0.18 W/m2K or better, which generally means at least 100mm of PIR insulation.
Insulation boards are laid with staggered joints to avoid cold bridges, and any gaps at the edges are filled or taped. The boards should be secured so they cannot shift during the membrane installation.
For EPDM rubber roofs, the membrane typically comes in a single large sheet, which is one of its biggest practical advantages. A single sheet means fewer joints, and joints are where flat roofs most commonly fail.
The membrane is rolled out, positioned, and then bonded to the insulation using a contact adhesive. The roofer works methodically from one side, folding the sheet back, applying adhesive to both surfaces, and pressing the membrane down. Particular care is needed at the corners and any upstands - the rubber has to be cut and formed neatly into internal and external angles without stretching or tearing.
Upstands (where the membrane turns up against a wall or parapet) should be a minimum of 150mm high. The top edge of the upstand is fixed with a termination bar and sealant. Any penetrations through the roof - outlets, pipes, ventilation ducts - are dressed with pre-formed EPDM collars bonded to the membrane.
Drip edges and trim around the perimeter are fitted in aluminium or galvanised steel, lapped to shed water clear of the fascia. This is often where a rushed job cuts corners: inadequate edge trim lets water run back under the membrane at the perimeter.
Drainage is the most important functional element of a flat roof. An outlet that is the wrong size, incorrectly positioned, or poorly sealed will cause ponding no matter how well the membrane is fitted.
Outlets are bonded into the membrane and should sit at the lowest point of the roof. Where a roof drains to a gutter at the perimeter, the drip edge needs to project far enough over the gutter to shed water cleanly. Internal outlets on larger roofs run through the structure to a downpipe - these need to be accessible for rodding and clearing.
Once drainage is in place, the roof should be checked for any low spots by running water across it. Any standing water after 48 hours indicates either a drainage problem or inadequate falls - both should be addressed before the job is signed off.
A completed flat roof should be walked by the roofer before they leave, checking all seams, upstands, edge trim, and outlets. The membrane surface should be free of wrinkles, bubbles, or areas where the bond has not taken. Edge trim should be tight to the fascia with no gaps.
All waste from the job - old felt, broken decking, packaging - should be removed from the site. Gutters should be checked and cleared, as debris from the strip-out commonly ends up in them.
You should be shown any sections of decking that were replaced, and receive an explanation of the system that has been installed: the membrane type, the insulation specification, and any relevant care instructions (for example, EPDM roofs can be walked on carefully for cleaning or maintenance, but sharp tools or heavy impact will damage them).
For most domestic flat roofs - extensions, garages, outbuildings - EPDM rubber is now the preferred choice. A well-installed EPDM membrane can be expected to last 40 to 50 years in normal conditions, compared with 10 to 15 years for a standard three-layer felt system. The material is UV-stable, highly flexible (so it handles thermal movement without cracking), and is available in large single sheets that minimise joints.
Mineral felt remains a cost-effective option where budget is the primary concern, and a properly installed high-performance torch-on felt system will give many years of reliable service. However, felt is more susceptible to blistering and cracking in temperature extremes, and the lap joints are more vulnerable to water ingress than a bonded EPDM membrane.
For a straightforward domestic extension in Cromer, a ballpark for EPDM installed on a warm roof deck runs from roughly £70 to £120 per square metre, depending on deck condition, access, insulation thickness, and number of penetrations. Felt replacement on a sound deck is typically cheaper per square metre but may need replacing sooner.
Not every flat roof problem needs a full replacement. Small areas of blistering or a single failed seam on a felt roof can sometimes be repaired with a compatible patching system or liquid waterproofing product. The question is whether a repair will hold, or whether the roof is at a point where ongoing repairs will cost more than a new installation over the next few years.
A repair is worth considering if the deck is sound, the roof is less than halfway through its expected life, and the damage is genuinely isolated. If the deck is soft in multiple areas, the felt is cracking across a wide area, or the roof has been patched more than once already, replacement is almost always better value.
For older flat roofs, a full strip and re-cover with EPDM tends to resolve the problem once rather than repeatedly.
If your flat roof is showing signs of trouble - damp patches on the ceiling below, standing water on the surface, or visible cracking and blistering - call us to arrange a proper roof survey. We will get up on the roof, tell you honestly what we find, and give you a clear written quote before any work is agreed.
No obligation · We'll call you to arrange a free visit
Call any time. Calls are answered day and night and passed straight to our roofers.
